Add bool item is_in_impl_trait to LoweringContext
Add bool item is_in_impl_trait to LoweringContext

This is for tracking if an ImplItem is part of a trait impl. Add
a with_trait_impl_ref method to ItemLowerer to appropriately save the
state to allow appropriate nesting of trait and non-trait impls.

graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust